In the blasting art, wherein a mixture of liquid and solid abrasive particles is blasted against a surface to effect a desired finishing thereof, it is conventional to provide the blasting nozzle with a shape which corresponds to the desired blasting pattern. For example, when it is desired to effect blasting of a flat rectangular pattern, the nozzle is provided with a cross-sectional shape which substantially corresponds to the pattern to be blasted. However, due to the abrasiveness of the solid particles which are being blasted through the nozzle, it has been observed that the nozzle undergoes rapid wear, and in fact substantial wear has been observed to occur in a matter of a few hours of operation, so that the cross-sectional shape of the nozzle undergoes substantial change. This has been observed even when the nozzle is constructed of a hard alloy. Further, the speed of the slurry (that is, the liquid-abrasive particle media) is not always uniform throughout the cross section of the nozzle in view of the different sectional configuration of the nozzle, and this also affects the uniformity of the media as it is being blasted onto the workpiece. This nonuniformity of flow also creates nonuniformity of wear, which also affects the shape and hence the blasting pattern. Accordingly, obtaining an even and uniform blasting, without encountering excessive nozzle wear, has been a long-standing and significant problem.
In addition, it is desirable to utilize this wet-blasting technique in an attempt to finish printed circuit boards, both to remove burr from the small drilled holes in the boards, and to also finish the surface of the board both before and after the circuit-making process. However, conventional nozzles have demonstrated an inability to provide uniformity of blasting sufficient to meet the requirements for finishing circuit board.
Accordingly, this invention relates to an improved nozzle designed specifically for blasting a wet abrasive slurry, which nozzle is capable of providing a substantially uniform blasting effect over a substantial area, and hence overcome many of the disadvantages associated with the prior nozzle structures. In addition, the improved nozzle is believed to provide such uniform blasting, and is believed capable of doing so over longer periods of time by providing a nozzle which creates more uniform flow velocity therethrough across the cross section thereof and at the same time is believed to experience less wear.
In the improved nozzle of the present invention, the nozzle body has an elongated flow passage extending transversely thereof and through which flows the slurry containing the abrasive particles. The bottom side of this flow passage is defined by angled surfaces which define a substantially V-shaped trough. A nozzle opening formed as an elongated slit communicates with the bottom of this trough, the slit being of narrow width but substantially elongated in the direction of the trough so as to permit discharge therethrough of a stream of slurry which is of a sheetlike configuration, that is, a wide but very narrow jet. An air nozzle number projects into the slurry passage throughout the elongated length thereof, the air nozzle member defining a narrow but longitudinally elongated air slit therethrough, with the tip of this slit being disposed within the V-shaped trough directly adjacent the inner end of the nozzle slit. The air nozzle member discharges a thin high-pressure curtain of air from the tip thereof directly into the bottom of the trough, causing the slurry to be blasted outwardly through the nozzle slit so as to create a thin sheetlike jet for impingement against a workpiece.
Other objects and purposes of the invention will be apparent to persons familiar with structures of this general type upon reading the following specification and inspecting the accompanying drawings.